Continuity mistake: In the first few scenes with the air cavalry commander, his black hat has a lieutenant colonel rank and a small crossed-sword emblem on it. Later, as his helicopter lands on the beach, his hat has no rank and is emblazoned with a very large crossed-sword Cav emblem. (00:27:26)
Continuity mistake: The Frenchmen with the accordion asks Captain Willard, "Do you know anything about Dien Bien Phu?". If you look closely at the doors in the other room, most of the lower shutters are closed. The next time we see them all as the Frenchman playing the accordion stands behind the captain and says, "Dien Bien Phu, okay" all the shutters are open even though no one goes near them. (02:08:30 - 02:10:00)????
Audio problem: On the French plantation dock Lance picks up what looks like the sole of an old shoe and smells it. If you look closely you hear a sniffing sound that isn't in sync with the movement of his chest because he doesn't really inhale while that horrible thing is near his nose. (01:57:05)????
Continuity mistake: As Captain Willard sits in the boat reading and thinking to himself about Colonel Kurtz he unwraps and eats a Hershey bar. He crumples the wrapper with both hands and throws it out of the boat, leaving nothing in his hands. In the next shot he's eating the Hershey bar again and the wrapper is back. (01:15:45)????
Continuity mistake: After Captain Willard looks at the picture of Colonel Kurtz being decorated by General Westmorland, they're all startled by the "Arc light" B-52 strike, note the rear machine gun is pointing forward and a helmet is hanging from the middle machine gun. In the next shot the rear machine gun is pointing aft and the helmet is now gone. (00:24:05)????
Continuity mistake: The actual napalm attack burns quite a large area of the tree line and just two shots later Colonel Kilgore speaks the famous lines, "I love the smell of napalm in the morning!" At this time, when we see this area is still smoking, quite heavily, however, the amount of destruction is much less and there is very little fire visible. (00:48:55)????